Particulate evacuation systems are employed in many particulate collection processes to transport and store the materials collected in those processes. For example, when coal is burned, the non-combustible portion of the coal, generally known as “fly ash” or “ash,” is removed from the exhaust gases in the coal-burning operation in order to prevent the fly ash from exiting the exhaust stack and fouling the environment. As another example, in the cement industry, a cement kiln has a lot of carryover dust, and a bag house or electrostatic precipitator is employed to prevent the dust from entering the environment. The potentially harmful particulate (e.g., fly ash, cement dust) is collected in hoppers from where they are recycled into the process or transported to larger and more permanent storage vessels. The invention herein focuses upon hopper evacuation systems in association with electrostatic precipitators, although it should be appreciated that general concepts herein are applicable to other particulate evacuation systems. The potential for expanding the concepts herein beyond electrostatic precipitators and to particulate collection and evacuation systems in general will be appreciated by those of ordinary skill in the art. Furthermore, the term “hopper” should be interpreted to apply to all types of particulate collection vessels, and not only those collection vessels specifically referred to as “hoppers” in the industry.
With reference to FIGS. 1-3, prior art particulate collection and evacuation systems, particularly hopper evacuation systems, are disclosed. These hopper evacuation systems are associated with electrostatic precipitators (FIG. 1), and, as noted above, need not be limited to this environment. In FIG. 1, electrostatic precipitator 10 includes electrically charged collection plate arrays 12, positioned above a plurality of hoppers 14. The collection plate arrays 12 are charged to attract and collect the particulate introduced to precipitator 10, for example, fly ash from a coal-burning operation. By rapping the arrays 12, the collected particulate is caused to fall and collect in hoppers 14. Hoppers 14 are organized in a grid pattern below the collection plate arrays 12, as is schematically depicted in FIGS. 2 and 3, where they are identified by a position number (position 1, position 2, position 3) in a given hopper row (row A, row B, row C). Usually, one hopper 14 will be associated with one collection plate array 12, although sometimes a hopper 14 may cover only a part of a given collection plate array 12 or may overlap and cover more than one collection plate array 12. Hoppers 14 cover the complete collecting area of electrostatic precipitator 10, such that all of the collected particulate is disposed in the hoppers 14, where they can be exhausted from the system.
In FIG. 2, a hopper evacuation vacuum system is schematically shown. In a vacuum system, hoppers 14 communicate directly with transport line system 16 through hopper outlet gates 18. The entire transport line system in under vacuum as a result of a vacuum source, generally represented by the numeral 20, that serves to transport particulate to a storage vessel 22. In the vacuum system, the contents of each hopper 14 are generally emptied one at a time, on a time-based or pressure-based cycle, so that there is never more than one hopper 14 emptying into transport line system 16 at any one time. Valves 24A, 24B, and 24C, respectively positioned in hopper row A, row B, and row C, selectively open and close the communication between their respective hopper row and vacuum source 20, such that the vacuum may be selectively applied to the row in which a hopper 14 is being emptied. When a given hopper 14, for instance the one at row A, position 1, is emptying to transport line system 16, the valves 24B and 24C associated with rows B and C (i.e., all rows other than row A) are closed so that only row A communicates with vacuum source 20. Thus, the particulate collected in the hopper 14 at row A, position 1, fall out of the hopper 14 and into the transport line system 16, and are transported to a storage vessel 22, such as a silo or ash pond. Some evacuation systems may have a different configuration of valves and piping.
In FIG. 3, a hopper evacuation pressure system is disclosed, and like parts between the vacuum system of FIG. 2 and the pressure system receive like numerals. Unlike hoppers 14 in the vacuum system, hoppers 14 of the pressure system associate with transport line system 16 through feeders 26. Functionally, these feeders 26 are similar to the hoppers 14 in the vacuum system inasmuch as they empty particulate to a transport line. Indeed, feeders and hoppers are considered herein to fall within the broad interpretation of the term “collection vessel(s).”
Feeders 26 are airlock type feeders, with inlet gates, herein termed “hopper outlet gates”28, and feeder outlet gates 30. Feeder vent lines 32 selectively communicate between each hopper 14 (or other low pressure source) and its associated feeder 26 through valves 34. To empty a hopper 14, the feeder vent line 32 associated with that hopper is opened at valve 34 to equalize the pressures within the hopper 14 (or other low pressure source) and its associated feeder 26. Thereafter, hopper outlet gate 28 is opened to feeder 26, and particulate within hopper 14 falls by gravity to feeder 26. After hopper outlet gate 28 is closed, feeder 26 is pressurized slightly above the pressure of transport line system 16, through a pressure source 36, feeder pressure line 38, and valve 37. Feeder outlet gate 30 is then opened, and the collected particulate flows by gravity and the slight pressure differential into transport line system 16. The entire transport line system 16 is pressurized by a system blower 40, that serves to transport particulate to a storage vessel 22. Similar to the vacuum system of FIG. 2, valves 24A, 24B, and 24C, respectively positioned in each hopper row A, row B, and row C, selectively open and close the communication between each respective hopper row and the system blower 40, such that the pressure supplied by the system blower 40 may be selectively applied to the row in which a feeder 26 is being emptied. Feeder outlet gate 30 is closed, and collected particulate is discharged into transport line system 16 and transported to storage vessel 22 by a positive pressure differential generated by system blower 40. In some embodiment, pressure source 36 and system blower 40 may be a common pressure source.
Such pressure and vacuum systems were historically controlled by a system of mechanical cam timers and relay logic. Many of these control systems have not changed since they were installed, sometimes as long as sixty years ago. As indicated, hopper evacuation is most often simply time based, with each hopper in each row emptying at a specific time in a repetitious cycle. Some hopper systems operate on rudimentary pressure feedback principals to adjust cycle time, and employ timers as a backup. Such control schemes do not account for the natural variations in particulate loading at each hopper, and offer little or no troubleshooting capabilities.
Hopper evacuation systems are being expected to perform in ways that originally were not intended. Changes in the amounts and characteristics of the particulate being handled by the systems require a better understanding of evacuation systems and a greater flexibility in system control. This flexibility and system performance analysis is not available in existing control methods, and most systems are not working at fill capacity for the current needs.
High maintenance troubleshooting is also an issue with these systems. System components are under constant pressure or vacuum, and air that is saturated with particulate matter is continuously flowing through the system. Problems with the piping or gates and valves are difficult to detect due to the closed nature of the system. It is difficult, if not impossible, to tell if the system is functioning incorrectly until a dangerously high volume of particulate collects in a hopper or feeder (collection vessel) as a result of a malfunctioning of the evacuation system. These high volume situations can create problems that are costly and dangerous to repair.
Thus, there is a need in the art for particulate collection systems that evacuate individual collection vessels based upon the collection of data rather than simple time-based or feedback-based sequences. There is also a need in the art of particulate collection and evacuation systems for a control system that can be monitored and that can troubleshoot a particulate evacuation system.